HYPOXIA INHIBITS COLD-INDUCED HUDDLING IN RAT PUPS

We asked to what extent hypoxia would modify the huddling behaviour of young rats during cold exposure. Sets of five animals (postnatal age 9 +/- 1 days) were placed at predetermined positions in a chamber main tained at similar to 33 degrees C (warm) or similar to 15 degrees C (c old), in normoxia or hypoxia (10% inspired O-2), and their movements m onitored for 30 min by a video camera. The surface areas (SA) of each individual pup (SAi) and of the whole set of pups (SAset) was measured every 5 min. In warm, the rats spread out, and both SAi and SAset wer e the greatest, whether in normoxia or hypoxia. In hypoxia, the total travelled distance (TTD) was much greater than in normoxia. In cold, d uring normoxia, SAi and SAset were decreased because of postural chang es and huddling, and body temperature, measured at the end of the expo sure, was also decreased. In hypoxic-cold, compared to normoxic-cold, fewer pups were in contact with one another, SAi and SAset did not dec rease and the drop in body temperature was larger. Differently from hy poxia, hypercapnia (5% CO2) did not modify the responses observed duri ng breathing air, whether in warm or cold conditions. We conclude that hypoxia, in addition to inhibiting shivering and non-shivering thermo genesis, can also limit behavioural thermogenesis, with the effect of further lowering body temperature. (C) 1998 Elsevier Science B.V. All rights reserved.